Many different approaches to the protection of personnel from life-threatening attacks exist. Examples include bullet-proof glass, concrete and steel building structures, armored cars, bullet-resistant jackets, and others. The particular avenue taken depends on whether the person to be protected is stationary, located in a vehicle, located within a building, or is required to maintain mobility outside the confines of any specific stationary structure.
For example, light-weight armor relies primarily on the strength and preferred placement of materials to defeat bullets or other projectiles. Thus, armor made of fabric material, such as nylon, aramids, or polyethylene, is designed to defeat lead-filled bullets, often called ball rounds. The conventional “bullet-proof” vest, however, cannot stop bullets that have hard cores. These types of bullets are often referred to as armor-piercing (AP) bullets. Currently, to defeat AP bullets, a layered structure element comprising a hard front face (e.g., ceramic) bonded to a metal or composite substrate element, is used. This combination of plates is inserted into pockets sewn into vests for body armor application. Alternatively, the combination of plates can consist of an integral element that has a shape somewhat conformable to the body. Such plates can also be attached to vehicles and other structures for protection of personnel.
Using the conventional multi-plate approach, material geometries and spacing between armor elements may be adjusted to induce ballistic projectiles to fracture and rotate about the incoming velocity vector. For example, one concept involves placing a multiplicity of holes within an armor element configuration. Given proper spacing between elements, the probability is great that an incoming projectile will strike the edge of a hole in the primary or first element, causing it to rotate before impacting the secondary or backup armor element. This approach requires a robust primary element so as to initiate rotation, and adequate air space between the primary and secondary elements to enable the projectile to rotate sufficiently before the second impact. Although effective as a system, it is difficult to decrease the weight of the primary element (while retaining performance), and a large air space is necessary between the primary element and the secondary element.
Lighter ceramics and improved substrate performance allow the production of reduced areal density elements, such that lighter armor can be produced to protect against a given threat. However, over the past twenty years, the decrease in areal density required to defeat AP threats has been incremental at best. New materials have resulted in small improvements in armor weight (i.e., areal density). To substantially reduce the weight of armor, including that worn by personnel, requires a significant decrease in areal density—much larger than that obtained to date.